Bushing temperature controller

ABSTRACT

A bushing temperature controller includes a transformer  3  which supplies a main current I 1  to the bushing  2  for accommodating molten glass, and regulation current supply units  7  and  8  which are adapted to supply regulation currents I 2  and I 3  either in phase with the main current I 1  or in phase inverted to the main current I 1  to a portion of a region to which the transformer  3  applies the current. Thus, the temperature control of partial regions  2   a  and  2   c  in the region to which the current is applied can be performed in a wide temperature range.

This application is a 371 of PCT/JP02/01300 filed on Feb. 15, 2002 hasbeen inserted thereof.

TECHNICAL FIELD

The present invention relates to a bushing temperature controller whichcontrols temperature of a bushing used for forming glass fiber.

BACKGROUND ART

Generally, glass fiber forming is performed in the following manner. Aplurality of orifices are formed on a bottom of a bushing whichaccommodates molten glass. Glass fibers are flown out through theorifices, and a plurality of the glass fibers are bundled and wound up.In this process, in order to obtain uniform glass fibers, the bushingneeds to be heated uniformly. The heating is performed by applying anelectric current to the bushing.

The bushing temperature control has hitherto been performed in such amanner that a thermoelectromotive force of a thermocouple arranged in acenter of the bushing is converted into a value of temperature and apredetermined amount of current is applied to the bushing so as to keepthe temperature constant.

However, both ends of the bushing tend to have high current densitiesand to have temperatures higher than the temperature in the center. Insuch a case, because of the non-uniform temperature distribution of thebushing, the Tex of the glass fibers flowing out from the bushingbecomes non-uniform, and quality defects are caused.

In order to prevent such a non-uniform temperature distribution of thebushing, the following techniques of controlling the bushing temperaturehave been proposed.

The Japanese Patent Laid-Open (Tokukai) No. S-61-228512 publicationdescribes a three-terminal controller for a bushing, which includes apower transformer for supplying a current to the whole of the bushing. Aregion to which the current is supplied is divided into two regions. Thethree-terminal controller allows a current applied to each dividedregion to be regulated by a current bypass circuit using a thyristor.This three-terminal controller for the bushing is designed to preventthe non-uniform temperature distribution of the bushing by regulatingamounts of the currents applied to the divided regions.

The Japanese Patent Laid-Open (Tokuhyou) No. H-2-500835 publicationdescribes a bushing temperature controller which includes first, second,and third power transformers. The first transformer supplies a currentto the whole of the bushing. A region to which the first transformersupplies the current is divided into three regions. The second and thirdpower transformers separately supply currents to the regions in bothends. This bushing temperature controller is designed to prevent thenon-uniform temperature distribution of the bushing by regulatingamounts of the currents applied to the regions in the both ends.

Furthermore, the Japanese Patent Laid-Open (Tokukai) No. H-11-327661publication describes a temperature controller which includes atransformer and shunt circuits. The transformer supplies a current tothe whole of the bushing. A region to which the transformer supplies thecurrent is divided into four regions. Each of the shunt circuitsbypasses the current flowing through each region. This temperaturecontroller is designed to facilitate segmentation of the region at lowcosts by forming the shunt circuits with wires and switches.

DISCLOSURE OF THE INVENTION

However, the bushing temperature controllers described above have thefollowing problems.

In the three-terminal controller for a bushing described in the JapanesePatent Laid-Open (Tokukai) No. S-61-228512 publication, the thyristorused for the current bypass circuit is a semiconductor device, thereforeit is difficult to locate the thyristor in the vicinity of the bushingwhich becomes heated. Accordingly, the location thereof is restricted.Moreover, in the three-terminal controller for a bushing, since theamount of the current applied to the bushing cannot be increased, avariable temperature range is narrow.

In the bushing temperature controller described in the Japanese PatentLaid-Open (Tokukou) No. H-8-22758 publication, the temperatureregulation is performed by separately supplying currents to the endportions of the bushing. Accordingly, to lower the temperatures at theend portions, it is necessary to reduce the amounts of the currentssupplied thereto. In the case that the amounts of currents are set tozero but the temperatures need to be further lowered, it is required toregulate the amount of the current supplied by the first powertransformer or to adjust a cooling fin located under the bushing forrapidly cooling the molten glass drawn out from a number of orifices.Accordingly, the operation of the temperature regulation becomescomplicated.

In the temperature controller described in the Japanese Patent Laid-Open(Tokukai) No. H-11-327661 publication, the amounts of current bypassedby the shunt circuits cannot be regulated. Accordingly, even when finetemperature control is to be carried out, hunting is caused, andvariation in Tex could be caused.

Therefore, the present invention is made to solve such technicalproblems. An object of the present invention is to provide a bushingtemperature controller which can easily perform temperature control ofthe bushing in a wide temperature range.

Specifically, a bushing temperature controller according to the presentinvention includes a main current supply unit for supplying a maincurrent to a bushing for accommodating molten glass; and a regulationcurrent supply unit which is adapted to supply a current for regulationeither in phase with the main current or in 180 degrees out of phasewith the main current to a portion of a region to which the main currentsupply unit applies the current.

The bushing temperature controller according to the present invention isprovided with at least two regulation current supply units. Each of theregulation current supply units supplies the current for regulation to aregion at each end of the region to which the main current supply unitapplies the current.

In the bushing temperature controller according to the presentinvention, the regulation current supply unit has a phase reversefunction of reversing a phase of the current to be supplied.

In the bushing temperature controller according to the presentinvention, the regulation current supply unit has a current changefunction of changing an amount of the current for regulation to besupplied.

According to the present invention, the current for regulation can besupplied in phase with the main current or in phase inverted to the maincurrent. Therefore, when the regulation current is supplied in phasewith the main current and the amount of the current applied to thepartial region of the bushing is increased to more than the maincurrent, the temperature can be regulated by heating. On the other hand,when the current for regulation is supplied in phase inverted to themain current and the amount of current applied to the partial region ofthe bushing is reduced to less than the main current, the temperaturecan be regulated by cooling. Therefore, by properly supplying thecurrent for regulation in phase with the main current or in phaseinverted to the main current, the temperature control can be performedin a wide temperature range. Consequently, the glass fiber forming canbe stably performed with no need to frequently change the amount of themain current, and the fiber forming can be thus efficiently performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a constitution of a bushing temperaturecontroller according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing a regulation current supply unitof the bushing temperature controller of FIG. 1.

FIG. 3 is a graph showing a result of actual temperature control in thebushing temperature controller according to the embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a description will be made of an embodiment of the presentinvention based on the accompanying drawings. In the drawings, the samecomponents are given the same reference numerals, and redundantdescription will be omitted. The dimensional proportions in the drawingsare not necessarily the same as those in the description.

FIG. 1 shows a schematic diagram of a constitution of a bushingtemperature controller according to the embodiment.

As shown in the drawing, a bushing temperature controller 1 according tothe embodiment is an apparatus performing temperature control of abushing 2, which controls temperature of the bushing 2 by supplying apredetermined current to the bushing 2 and regulating an amount of theapplied current. The bushing 2 is a container which accommodates moltenglass. The molten glass is flown out from a number of orifices (notshown) formed on a bottom of the bushing 2 to form fibers. The bushing 2is composed of a conductive material, for example, platinum, an alloythereof, or the like.

The bushing temperature controller 1 includes a transformer 3 whichsupplies a current to the bushing 2. The transformer 3 functions as maincurrent supply means for supplying a main current I1 to the whole of thebushing 2 and uses, for example, a power transformer. A primary winding3 a of the transformer 3 is connected to a power controller 4. The powercontroller 4 controls an output of the transformer 3. The powercontroller 4 is connected to a power line 5 as an alternating currentsource and receives power supply from the power line 5.

At both ends of the bushing 2, input terminals 21 and 22 are provided.The input terminals 21 and 22 are connected to a secondary winding 3 bof the transformer 3 and receive supply of the main current 11 from thetransformer 3. The bushing 2 is provided with intermediate terminals 23and 24. The intermediate terminals 23 and 24 are arranged between theinput terminals 21 and 22. A region of the bushing 2 between the inputterminals 21 and 22 is equally divided into three regions, which are afirst region 2 a, a second region 2 b, and a third region 2 c startingfrom a side of the input terminal 21. The intermediate terminal 23 islocated at a boundary between the first and second regions 2 a and 2 b.The intermediate terminal 24 is located at a boundary between the secondand third regions 2 b and 2 c.

In the second region 2 b of the bushing 2, a temperature sensor 32 islocated. The temperature sensor 32 is a temperature detection means fordetecting temperature of the second region 2 b, which is the middleregion of the bushing 2, and uses, for example, a thermocouple. Thetemperature sensor 32 is connected to a temperature control unit 62 andoutputs a temperature detection signal to the temperature control unit62. The temperature control unit 62 outputs a control signal to thepower controller 4 based on the temperature detection signal of thetemperature sensor 32.

The bushing temperature controller 1 includes regulation current supplyunits 7 and 8. The regulation current supply units 7 and 8 areregulation current supply means for allowing a current for regulation tobe supplied in phase with the main current I1 or in phase inverted tothe main current I1 to a portion of a region to which the transformer 3applies the current. The regulation current supply unit 7 is connectedto the input terminal 21 and the intermediate terminal 23 and supplies aregulation current I2 in phase with the main current I1 or in phaseinverted to the main current I1 to the first region 2 a, which is thepartial region of the region to which the transformer 3 applies thecurrent. The regulation current supply unit 7 will be described later indetail.

The regulation current supply unit 8 is connected to the input terminal22 and the intermediate terminal 24 and supplies a regulation current I3in phase with the main current I1 or in phase inverted to the maincurrent I1 to the third region 2 c, which is the partial region of theregion to which the transformer 3 applies the current.

In the first region 2 a of the bushing 2, a temperature sensor 31 islocated. The temperature sensor 31 is a temperature detection means fordetecting temperature of the first region 2 a, which is an end region ofthe bushing 2, and uses, for example, a thermocouple. The temperaturesensor 31 is connected to a temperature control unit 61 and outputs atemperature detection signal to the temperature control unit 61.

In the third region 2 c of the bushing 2, a temperature sensor 33 islocated. The temperature sensor 33 is a temperature detection means fordetecting a temperature of the third region 2 c, which is the end regionof the bushing 2 and, for example, uses a thermocouple. The temperaturesensor 33 is connected to a temperature control unit 63 and outputs atemperature detection signal to the temperature control unit 63.

FIG. 2 shows a diagram showing the constitution of the regulationcurrent supply unit 7.

As shown in the drawing, the regulation current supply unit 7 includes atransformer 71 which supplies a current between the input terminal 21and the intermediate terminal 23. A secondary winding 71 a of thetransformer 71 is connected to the input terminal 21 and theintermediate terminal 23 of the bushing 2. The primary side of thetransformer 71 is constituted by connecting primary windings 71 b and 71c in series.

One end of the primary winding 71 b is connected to a power regulator72, and the other end thereof is connected to an intermediate tap 71 d.The power regulator 72 regulates a power amount of the primary winding71 b and is constituted by using, for example, a switching device suchas thyristor. The input side of the power regulator 72 is connected toan electric wire 5 a of the power line 5. The power line 5 is composedof two electric wires of the electric wire 5 a and an electric wire 5 b.

The intermediate tap 71 d is an intermediate terminal located betweenthe primary windings 71 b and 71 c. The intermediate tap 71 d isconnected to the electric wire 5 b of the power line 5.

One end of the primary winding 71 c is connected to a power regulator73, and the other end thereof is connected to the intermediate tap 71 d.The power regulator 73 regulates a power amount of the primary winding71 c and is constituted, for example, by using a switching device suchas a thyristor, similarly to the power regulator 72. The input side ofthe power regulator 73 is connected to the electric wire 5 a of thepower line 5.

The regulation current supply unit 7 includes a control unit 74. Thecontrol unit 74 outputs control signals to the power regulator 72 and 73based on an output signal from the temperature control unit 61 andcontrols activation of the power regulators 72 and 73. For example, thecontrol unit 74, based on the output signal from the temperature controlunit 61, activates one of the power regulators 72 and 73 and inactivatesthe other to set the regulation current I2, which is the output currentfrom the regulation current supply unit 7, to a current in phase withthe main current I1.

Further, the control unit 74 inactivates one of the power regulators 72and 73 and activates the other to set the regulation current I2 to acurrent in phase inverted to the main current I1. Furthermore, thecontrol unit 74 inactivates both of the power regulators 72 and 73 toset the regulation current I2 to zero.

Based on the control signal of the control unit 74, the amounts ofcurrent through the power regulators 72 and 73 and the amounts ofcurrent through the primary windings 71 b and 71 c and the secondarywinding 71 a are regulated, and the regulation current I2 of theregulation current supply unit 7 is thus controlled.

The regulation current supply unit 8 is constituted similarly to theabove described regulation current unit 7 and operates similarly.Specifically, the regulation current supply unit 8 includes atransformer (not shown) which supplies a current between the inputterminal 22 and the intermediate terminal 24. The regulation currentsupply unit 8, based on the output signal from the temperature controlunit 62, properly changes a direction of a current on the primary sideof the transformer and outputs the regulation current I3 in phase withthe main current I1 or in phase inverted to the main current I1.

Next, a description will be made of an operation of the bushingtemperature controller according to the embodiment.

In FIG. 1, first, the temperature of the bushing 2 is set in accordancewith a diameter of glass fibers to be formed by the bushing 2. Thesetting of the temperature is performed by setting heating temperaturesat the temperature controllers 61, 62, and 63.

The temperature control unit 62 activates the power controller 4 and thetransformer 3 based on the set temperatures and the output signal fromthe temperature sensor 32. With the activation of the power controller 4and the transformer 3, the main current I1 is applied to the first,second, and third regions 2 a, 2 b, and 2 c between the input terminals21 and 22 of the bushing 2. The bushing 2 is thus heated.

In this process, if the temperature of the second region 2 b of thebushing 2 is lower than the set temperature, the output from thetransformer 3 is increased. Accordingly, the main current I1 isincreased, and the temperature of the bushing 2 rises. On the otherhand, when the temperature of the second region 2 b of the bushing 2 ishigher than the set temperature, the output from the transformer 3 isreduced. Thus, the main current I1 is reduced, and the temperature ofthe bushing 2 drops.

Meanwhile, the temperature control unit 61 activates the regulationcurrent supply unit 7 based on the set temperature and the output signalfrom the temperature sensor 31. With the activation of the regulationcurrent supply unit 7, the regulation current I2 is applied to the firstregion 2 a between the input terminal 21 and the intermediate terminal23 of the bushing 2. Thus, the total amount of current applied to thefirst region 2 a becomes a sum of the main current I1 and the regulationcurrent I2.

In this process, if the temperature of the first region 2 a of thebushing 2 is lower than the set temperature, the regulation current I2outputted from the regulation current supply unit 7 is set to be inphase with the main current I1. Thus, the amount of current applied tothe first region 2 a is increased, and the temperature of the firstregion 2 a rises. On the other hand, when the temperature of the firstregion 2 a of the bushing 2 is higher than the set temperature, theregulation current I2 outputted from the regulation current supply unit7 is set to be in phase inverted to the main current I1. Thus, theamount of current applied to the first region 2 a is reduced, and thetemperature of the first section 2 a drops.

In such a manner, by properly supplying the regulation current I2flowing in the first region 2 a of the bushing 2 in phase with the maincurrent I1 or in phase inverted to the main current I1, the temperaturecontrol of the first region 2 a as the end region of the bushing 2 canbe performed in a wide temperature range.

Accordingly, it is unnecessary to frequently change the amount of themain current I1 in accordance with the diameter of the glass fibers tobe manufactured, and the glass fiber forming can be stably performed.Thus, the fiber forming can be efficiently performed. Moreover, thetransformer 71 of the regulation current supply unit 7 can use atransformer having a low rating, and costs of the bushing temperaturecontroller 1 can be reduced.

Note that when the temperature of the first region 2 a of the bushing 2is the same as the set temperature, the regulation current I2 outputtedfrom the regulation current supply unit 7 is set to zero. In this case,the amount of current applied to the first region 2 a does not change,and the temperature of the first region 2 a is maintained.

The temperature control unit 63 activates the regulation current supplyunit 8 based on the set temperature and the output signal from thetemperature sensor 33. With the activation of the regulation currentsupply unit 8, the regulation current I3 is applied to the third region2 c between the input terminal 22 and the intermediate terminal 24 ofthe bushing 2. Thus, the total amount of current applied to the thirdregion 2 c becomes a sum of the main current I1 and the regulationcurrent I3.

In this process, when the temperature of the third region 2 c of thebushing 2 is lower than the set temperature, the regulation current I3outputted from the regulation current supply unit 8 is set to be inphase with the main current I1. Thus, the amount of current applied tothe third region 2 c is increased and the temperature of the thirdregion 2 c rises. On the other hand, when the temperature of the thirdregion 2 c of the bushing 2 is higher than the set temperature, theregulation current I3 outputted from the regulation current supply unit8 is set to be in phase inverted to the main current I1. Thus, theamount of current applied to the third region 2 c is reduced and thetemperature of the third region 2 c drops.

In such a manner, by properly supplying the regulation current I3flowing in the third region 2 c of the bushing 2 in phase with the maincurrent I1 or in phase inverted to the main current I1, the temperaturecontrol of the third region 2 c as the end region of the bushing 2 canbe performed in a wide temperature range.

Accordingly, it is unnecessary to frequently change the amount of themain current I1, and the glass fiber forming can be stably performed.Thus, the fiber forming can be efficiently performed. Moreover, thetransformer of the regulation current supply unit 8 can use atransformer having a low rating, and costs of the bushing temperaturecontroller 1 can be reduced.

Note that when the temperature of the third region 2 c of the bushing 2is the same as the set temperature, the regulation current I3 outputtedfrom the regulation current supply unit 8 is set to zero. In this case,the amount of current applied to the third region 2 c does not change,and the temperature of the third region 2 c is maintained.

FIG. 3 shows a result of the temperature control when the bushingtemperature controller according to the embodiment is actually operated.

In FIG. 3, the axis of abscissas represents a position along thedirection of the current applied to the bushing 2, and the axis ofordinates represents a temperature difference from a predeterminedreference temperature. For the bushing 2 subjected to the temperaturecontrol, a bushing which was made of an alloy of 90% of platinum and 10%of rhodium was used. The bushing was box-shaped and included 1200orifices for drawing out the molten glass on the bottom thereof.

As shown in the drawing, when only the set temperature of the firstregion 2 a was lowered by 30° C. (line connecting circles: ∘-∘), thetemperature of the first region 2 a became about 30° C. lower than thetemperatures of the second and third regions 2 b and 2 c. When the settemperatures of the first and third regions 2 a and 2 c were lowered by30° C. (line connecting triangles: Δ-Δ), the temperatures of the firstand third regions 2 a and 2 c became about 30° C. lower than thetemperature of the second region 2 b.

When the set temperatures of the first and third regions 2 a and 2 cwere raised by 30° C. (line connecting squares: □-□), the temperature ofthe first and third regions 2 a and 2 c became about 30° C. higher thanthe temperature of the second region 2 b. When only the set temperatureof the second region 2 b was raised by 30° C. (line connectingrhombuses: ⋄-⋄), the temperature of the second region 2 b became about20° C. higher than the temperature of the first and third regions 2 aand 2 c.

Such results reveal that the temperature can be regulated according tothe theory by the application of the regulation current in phase withthe main current or in phase inverted to the main current.

As described above, according to the bushing temperature controller 1 ofthe embodiment, the regulation currents I2 and 13 can be supplied inphase with the main current I1 or in phase inverted to the main currentI1. Therefore, when the regulation currents I2 and 13 are supplied inphase with the main current I1 and the amount of the current applied tothe partial region of the bushing 2 is increased to more than the maincurrent I1, the temperature can be regulated by heating. Moreover, whenthe regulation currents I2 and I3 are supplied in phase inverted to themain current I1 and the amount of current applied to the partial regionof the bushing 2 is reduced to less than the main current I1, thetemperature can be regulated by cooling. Therefore, by properlysupplying the regulation currents I2 and I3 in phase with the maincurrent I1 or in phase inverted to the main current I1, the temperaturecontrol can be performed in a wide temperature range. Consequently, theglass fiber forming can be stably performed with no need to frequentlychange the amount of the main current, and the fiber forming can bestably performed.

In the embodiment, the description has been made of the case where theregion of the bushing 2 to which the current is applied is divided intothree regions, but the bushing temperature controller according to thepresent invention is not limited to such a case. The region of thebushing 2 to which the current is applied may be divided into two, four,or more regions, and the bushing temperature controller may apply theregulation current to a part of the divided regions in phase with themain current or in phase inverted to the main current. Also in thiscase, operational advantages similar to those of the bushing temperaturecontroller according to the embodiment can be obtained.

INDUSTRIAL APPLICABILITY

The present invention is applicable in the glass fiber forming.

1. A bushing temperature controller, comprising: a main current supplyunit which supplies a main current to a bushing for accommodating moltenglass; and a regulation current supply unit comprising a transformer;the primary side of said transformer comprising two primary windings,wherein the electric power is separately supplied to each of saidprimary windings so that the phase of the electric current applied toone of said primary windings is opposite to that of the other; theregulation current supply unit further comprising two regulators, whichregulate the electric power into said primary windings respectively; theregulation current supply unit further comprising a control unit, whichoutputs a control signal to said regulators; said regulators receivingthe control signal separately; wherein at least two regulation currentsupply units are provided and each of the regulation current supplyunits supplies the current for regulation to a region at each end of theregion to which the main current supply unit applies the current; andwherein said primary windings are connected in series.
 2. The bushingtemperature controller according to claim 1, wherein the regulationcurrent supply unit includes a current change function of changing anamount of the current for regulation to be supplied.
 3. A bushingtemperature controller, comprising: a main current supply unit whichsupplies a main current to a bushing for accommodating molten glass; anda regulation current supply unit comprising a transformer; the primaryside of said transformer comprising two primary windings, wherein theelectric power is separately supplied to each of said primary windingsso that the phase of the electric current applied to one of said primarywindings is opposite to that of the other; the regulation current supplyunit further comprising two regulators, which regulate the electricpower into said primary windings respectively; the regulation currentsupply unit further comprising a control unit, which outputs a controlsignal to said regulators; said regulators receiving the control signalseparately; wherein at least two regulation current supply units areprovided and each of the regulation current supply units supplies thecurrent for regulation to a region at each end of the region to whichthe main current supply unit applies the current; wherein said primarywindings are connected in series; and wherein during operation of thebushing temperature controller, both of the two primary windings arenever simultaneously supplied with power.
 4. The bushing temperaturecontroller according to claim 3, wherein the regulation current supplyunit includes a current change function of changing an amount of thecurrent for regulation to be supplied.